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Rouzbeh Amini, Anup Pant, Rodolfo Repetto, Syril Dorairaj; A computational parametric analysis of the effects of the size and location of the laser peripheral iridotomy on the aqueous humor pressure following pupil dilation. Invest. Ophthalmol. Vis. Sci. 2019;60(9):2244. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Assess outcomes of laser peripheral iridotomy (LPI) procedures by estimating the pressure difference between the anterior and posterior chambers of the iris for different hole sizes/locations.
A three-dimensional finite element model of the iris similar to our previous two-dimensional axisymmetric model (IOVS, 59: 4134-4142) was created using geometry obtained from anterior segment optical coherence tomography images. A dilator region of 0.2 mm was manually identified in which the dilator stress was applied to simulate pupillary dilation. Holes with diameters of 200 μm and 400 μm were made near the pupillary margin, at the mid-periphery, and at the periphery of the iris to simulate LPI. The pressure difference developed across each hole before/after pupil dilation was computed using computational fluid dynamics methods, first by considering the iris as a compressible material and then as a nearly incompressible material.
The pressure difference developed across a 200-μm hole when the hole was placed near the pupil, at the iris mid-periphery, and near the iris periphery was 0.85 Pa, 0.80 Pa, and 0.92 Pa, respectively. Following pupil dilation, the pressure difference increased in all cases (Table 1). For the compressible model, the pressure increased by 4.70%, 63.75%, and 52.17% near the pupil, at the iris mid-periphery, and near the iris periphery, respectively. For the nearly incompressible model, the pressure increased by 7.06%, 51.25%, and 55.43% near the pupil, at the iris mid-periphery, and near the iris periphery, respectively. The difference in pressure developed when using a 400-μm diameter hole was extremely small, both before and following dilation (Table 2).
While LPI is widely used for narrow or closed anterior chamber angles (ACA), in certain patient populations, the ACA remains occludable even after LPI. One possible reason for such complications could be the additional pressure difference developed across the anterior and posterior chamber as a result of changes in the LPI hole size following dilation-induced iris deformation. Our study shows that the LPI hole size/location has a pronounced effect (especially in the the iris mid-periphery and near the iris periphery) in both compressible and nearly incompressible irides.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
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